Over the past several decades, polymer blend technology has achieved an important position in the field of polymer science from both a scientific and technology viewpoint. With regard to binary component blends, a large number of possibilities exist in which either miscibility or immiscibility is observed. Superimposed on these myriad of possibilities is the likelihood that one or both of the components are crystalline.
Typically, blends with crystallizable components are generally heterogeneous below the melting temperature. In fact, it has been noted, compatible blends within these systems would require the formation of mixed crystals in which both polymer chains would cocrystallize. Therefore, if miscibility would occur, it would occur in the amorphous phases since cocrystallization is an unlikely occurrence.
The literature also teaches that tough amorphous-type blends could be formed with the "addition" of low levels of interacting functionalities. Ionic groups, especially transition metal neutralized sulfonate or carboxylate groups, are able to coordinate with a wide variety of bases, such as 4-vinylpyridine, contained within a separate copolymer structure. The initial thrust focussed on the incorporation of rubbery materials into an amorphous, brittle matrix. The physical properties, especially toughness, were dramatically enhanced through these coordination-type interactions. More recently, a similar approach was utilized to enhance the properties of semicrystalline polymers, specially polyethylene. In both of the above mentioned family of blends, interactions between otherwise immiscible components, resulted in markedly improved properties. The level of functionality was typically less than 10 mole percent, which is not sufficient for forming completely miscible systems. As anticipated, the nature of the transition metal counterion had a marked influence on the blend properties. Non-transition metal counterions, such as sodium, for blend systems have poor properties closely approximating those found in unfunctionalized, noninteracting blends.
The unblended metal neutralized ionomeric materials previously described also have interesting solution and bulk properties. The incorporation of even very low levels of ionic groups profoundly influences properties through both intra- and inter-molecular associations. It is now virtually indisputable that low order aggregates and clusters exist in some form in the bulk state. The exact nature of the ion-rich regions, however, are still an object of considerable debate. It is certain that in ion-containing polymers with low ion concentration, the ionic groups aggregate as multiple ion pairs which give the polymer properties similar to a crosslinked system. The junction points are due to physical interactions (and not to chemical bonding). Furthermore, a critical concentration is reached where the properties become dominated by ionic clusters or aggregates of multiplets.
In this invention, solution blending was used to prepare semicrystalline blends containing an ionomeric polyethylene, specifically ethylene-methacrylate copolymer, and an amorphous component, specifically metal neutralized sulfonated ethylene-propylene diene rubber. Melt blending was also an effective blending technique. The instant invention details formation of blends through the interaction of ion-containing copolymers. The ionically-associating units are located on otherwise immiscible blend systems. In the blend compositions described here, the ionomeric associations are purely coulombic in nature and not specific interactions as in blends formed through coordination-type complex formation. These compositions are useful in a variety of structural automotive, medical, packaging applications and the like.